The present invention relates generally to generator powered electrically heated catalyst systems and more specifically to generator powered electrically heated catalyst systems for automotive applications.
Modern internal combustion powered vehicles utilize a catalytic converter in the exhaust system. This converter by means of chemical reactions converts much of what would otherwise be undesirable exhaust gases into carbon dioxide and water. This has been a preferred solution, and unleaded gasoline permits the use of catalytic converters in automotive applications, since catalytic converters cannot tolerate any lead content in the exhaust fumes.
Today cars are so clean burning that most of the undesirable exhaust emissions at the output of the catalytic converter occurs within the first few minutes of engine operation from a cold start. This occurs because the catalytic converter does not operate at peak efficiency when it is cold, and a warm-up time of about ten minutes from a cold start is typically required before peak catalytic converter efficiency is reached and maintained. Current legislation dictates that these few minutes of relatively high emissions must be minimized. This establishes the need to artificially heat the catalytic converter quickly upon a cold start.
One method known in the prior art to accomplish this involves injecting a rich air/fuel mixture into the combustion chamber which will exhaust a high hydrocarbon exhaust gas. Oxygen is then injected into the exhaust pipe, causing the heated hydrocarbon rich mixture to ignite in the exhaust pipe before reaching the catalytic converter. This superheated gas then passes through the catalytic converter causing it to heat quickly. This method requires the addition of an air pump, which is cumbersome and draws power from the engine at all times, unless an electrical pump is utilized and cycled by electrical techniques. Air pumps are not known for good reliability, and would present challenges to meeting 100,000 mile exhaust emission system reliability goals.
Other methods are known in the prior art for causing quick initial heating of the catalytic converter. One example is the oversized crystal controlled oscillator common to electronics. When initially powered on from a cold start, the oversized crystal controlled oscillator utilizes an internal feedback loop which applies maximum heating power to its heating elements, gradually reducing this power as the desired temperature operating point is approached. Another prior art example is the technique utilized to achieve quick heating of windshields in cold environmental conditions, wherein unregulated electrical power is applied to the heating element. This heating system is elemental, and the heating voltage is sawtooth in nature with a high peak-to-valley ratio as the power delivered to the windshield heaters does not have to be accurately known.
No other prior art method to electrically heat automotive catalytic converters is known.
The method of the present invention involves interfacing with the electrical charging systems of automobiles as commonly known to the art. For that reason a basic description of a typical prior art automotive electrical charging system follows.
The charging system maintains a constant voltage to the electrical system of the automobile. This voltage is regulated by means of a feedback loop which utilizes a generator, bridge rectifier, and voltage regulator. The voltage regulator controls the amount of excitation current present in the field windings of the generator. The speed of rotation of the generator and the amount of field current determine the amount of power supplied by the generator/bridge rectifier to the automotive electrical system. The amount of field current is controlled by the voltage regulator, which monitors the voltage level in the electrical system and adjusts the field current in a manner so as to maintain the constant voltage.
Modern voltage regulators are of various constructions, and may be of monolithic, hybrid or printed circuit types. Several regulator features require discussion here because they are utilized by the present invention. These are reduced setpoint regulation, external or battery sensing, and overvoltage regulation protection.
Reduced setpoint regulation is commanded by providing a logic low signal to the Lamp (L) input terminal of the voltage regulator. During normal rotation of the generator, if the L terminal is brought low the regulator will establish a regulation set point of 75% of the "normal" regulation set point. Regulators also contain an ignition (I) input terminal which functions similarly, but only the L input terminal will be discussed.
Regulators have the ability to sense the battery voltage via a specialized input Sense (S) terminal. Remote sensing allows for more accurate remote voltage sensing because the S input typically is designed to have a relatively high input resistance.
Overvoltage regulation protection is required if, for some reason, the output of the generator is disconnected from the vehicle's electrical system. What then happens is that the S terminal sees a drop in voltage due to the generator no longer providing energy to the electrical system (which includes the battery) and commands full excitation current in the generator field windings. This causes a maximum output condition of the generator. With the output of the generator disconnected from the electrical system (which is the generator load) the output of the generator is uncontrolled and can go to the limits of the generator. This may cause catastrophic damage to the internal parts of the generator and other loads connected thereto, which is not acceptable. The overvoltage protection feature will not allow the Vgo terminal to go above a specified voltage level by limiting the field current if this level starts to be exceeded. This restriction on field current is reduced as the voltage on the Vgo terminal starts to reduce, thus establishing a pseudo regulation point at what is termed the overvoltage threshold.
Increasingly stringent exhaust emission regulations require that emitted pollutants occurring during cold start be reduced. An electrical solution wherein the catalytic converter is quickly heated, by simple electrical means, is seen as the most viable and economical solution, but prior art does not teach the required electrical heating technique for automotive catalytic converters. There is thus an unmet need in the art to describe a technique wherein electrical techniques are utilized in a simple and economical manner to heat automotive catalytic converters quickly in cold-start conditions, thereby reducing exhaust emissions.